Aromatics extraction process

ABSTRACT

AROMATICS ARE EXTRACTED FROM AROMATICS-CONTAINING HYDROCARBON MIXTURES BY CONTACTING SAID MIXTURES WITH A SOLVENT COMPRISING 2-(2-AMINOETHOXY) ETHANOL CONTAINING WATER IN AMOUNTS FROM ABOUT 0.7-10 PERCENT, BY VOLUME.

United States Patent 3,733,262 AROMATICS EXTRACTION PROCESS Michael R. Basila, Munster, Ind., and Alfred R. Pate, Jr., Tyler, Tex., assignors to Howe-Baker Engineers, Inc., Tyler, Tex.

No Drawing. Continuation-impart of application Ser. No. 752,740, Aug. 15, 1968, now Patent No. 3,583,906. This application Feb. 16, 1971, Ser. No. 115,864 The portion of the term of the patent subsequent to June 8, 1988, has been disclaimed Int. Cl. 010g 21/16 US. Cl. 208-331 Claims ABSTRACT OF THE DISCLOSURE Aromatics are extracted from aromatics-containing hydrocarbon mixtures by contacting said mixtures with a solvent comprising 2-(2-aminoethoxy) ethanol containing water in amounts from about 0.7-10 percent, by volume.

CROSS-REFERENCE TO RELATED APPLICATIONS This invention is a continuation-in-part of a copending application entitled Aromatic Extraction Process; filed Aug. 15, 1968; Ser. No. 752,740; now Pat. No. 3,583,906 assigned to Howe-Baker Engineers, Inc., by Michael R. Basila and Alfred R. Pate, r.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION It has now been found that aromatics are extracted from aromatics-containing hydrocarbon mixtures by a process comprising contacting said mixture with an aqueous solution of 2-(2-aminoethoxy) ethanol containing from about 0.7 to 10 percent water, by volume, for a time sufficient to extract substantial quantities of aromatics from said aromatics-containing mixture.

By practicing this invention, aromatics can be extracted from a reformed naphtha stream and subsequently separated into high purity benzene, toluene and xylene products. Similarly, high octane aromatics can be separated from hydrocarbon mixtures and used for motor fuel blending purposes. Alternatively, or simultaneously, low aromatic raffinates can be produced as jet fuel components, high smoke point kerosenes, or specialty solvent products. Specific examples of applications to which this invention is useful include extraction of aromatics from jet fuel or kerosene to improve the burning quality, smoke point and heat of combustion; extraction of aromatics from diesel to improve burning quality and diesel index; extraction of aromatics from light catalytic cyclic oil for upgrading to diesel; and extraction of aromatics from solvents to comply with pollution control standards.

It has been found that the addition of water to 2-(2- aminoethoxy) ethanol does not substantially affect the 3,733,262 Patented May 15., 1973 capacity of 2-(2-aminoethoxy) ethanol for aromatics, within certain volume ranges of water, while at the same time its selectivity (i.e. the afi'inity or preference of the solvent for aromatics as compared with non-aromatics) is greatly enhanced. This discovery is quite unexpected in light of prior art teachings which disclose that the capacity of aromatics extraction solvents is adversely affected by the addition of water.

Above about ten percent, by volume, of water with Z-(Z-aminoethoxy) ethanol tends to diminish the aromatics extraction efliciency of the solvent solution, but its selectivity is increased with addition of water throughout the range from about 0.7 to 10 percent water, by volume. Thus, it has been found that solvent solutions of 2-(2-aminoethoxy) ethanol containing from about0.7 to 10 percent water, by volume, are effective aromatics ex traction solvents. The capacity of the solvent solution is substantially unaffected throughout certain ranges of water addition while the selectivity of the solvent solution is increased by increasing the amount of water added within these ranges.

For the vast majority of aromatic-containing hydrocarbon mixtures from which it is desired to extract aromatics, the capacity of the solvent solution of 2-(2-aminoethoxy) ethanol and water for aromatics decreases rapidly when the water content exceeds about 10 percent, by.

volume. The addition of a small amount of water, e.g. about 0.7 percent, by volume, does, however, increase selectivity.

To a degree, the desired amount of water added to make the aqueous solution of 2-(2-aminoethoxy) ethanol will depend upon the type of aromatic contained in the feedstock to which the extraction is directed. In general, the capacity of the aqueous solution for an aromaticcontaining hydrocarbon mixture rich in light aromatics (e.g. benzene) will be substantially unalfected thoughout the 0.7-1O percent range while the capacity of the aqueous solution for a heavy aromatic-rich stream (e.g. C aromatics or higher) will be affected somewhere within the 0.7-l0 percent range, e.g. from about l-5 percent water, by volume. Thus, in general, depending upon the particular aromatic-containing hydrocarbon mixture, it would be desirable to employ aqueous solutions of Z-(Z-aminoethoxy) ethanol and water containing from about 0.7-10 percent water; 1-10 percent water; 0.7-5 percent Water; 5-10 percent water; 3-8 percent water; 49 percent water; 5-7 percent water; 58 percent water; 5-9 percent water; and the like, all by volume. Of course, it may be advantageous at times to employ about 1, 2, 3, 4 or 5 percent water, by volume and similarly 6, 7, 8, 9 or 10 percent water, all by volume.

Since typical aromatic-containing hydrocarbon streams will contain mixtures of benzene, toluene and xylenes as well as C, aromatics and greater in various percentages, it is necessary to vary the water content of the aqueous solution of 2-(2-aminoethoxy) ethanol within the 0.7 to 10 percent water range, by volume, in order to determine the most economical range of operation. It is most desirable to fix the amount of water so that the capacity for a particular aromatic or aromatic mixture to which the extraction is primarily directed, is not substantially affected but not much more than is so required to attain required purity so as to avoid excess utility costs involved in pumping and in vaporizing excess water in the extract Stripper.

In order to practice the invention, conventional aromatics extraction process techniques which are well known in the art are employed.

Typically, a feed stream of an aromatics-containing hydrocarbon mixture is heated to extraction temperature, e.g. from about 250325 F. depending upon its composition, by known techniques such as a steam charge heater, and thereafter enters into a conventional multi-stage liquid-liquid extractor at an intermediate point or points. The aqueous solvent mixture of 2-(2-aminoethoxy) ethanol containing about 0.7- percent water, by volume, enters the extractor at the top and flows downwardly therethrough so as to mix and countercurrently contact with the rising hydrocarbon feed thereby extracting aromatics from the feed. Most of the aromatics in the feed are extracted by the solvent, leaving a hydrocarbon phase having a very low aromatic content, referred to as the raflinate. The raflinate is removed from the top of the extractor and the rich solvent, containing the extracted aromatics and some light non-aromatics, is withdrawn from the bottom of the extractor.

The rich solvent leaving the extractor is typically flashed at least once to separate light hydrocarbons to be removed and thereafter the rich solvent is fed to a conventional stripper. Overhead vapors from the stripper are removed, combined with flash vapors and thereafter condensed. The resulting liquid stream contains large amounts of light non-aromatics and is typically recycled back to the bottom of the extractor to displace heavier non-aromatics from the solvent so as to avoid having heavier non-aromatics in the extract. As is Well known, heavy non-aromatics in the extract cause loss of product purity because of similar relative volatilities to the typical desired products.

The desired products, e.g. benzene, toluene, xylenes, ethylbenzene, and the like, are removed in mixtures as a side out from the stripper. They are typically thereafter separated by well known distillation techniques.

The aromatics depleted solvent is removed from the bottom of the stirpper, adjusted to contain the proper amount of water and thereafter recycled back to the top of the extractor as lean solvent.

The above-described processing techniques which employ liquid-liquid extraction and extractive distillation, are well known in the art. The operating characteristics and design of the extractor, stripper and subsequent purification systems are also well known in the art.

Typical extraction temperatures for most aromaticscontaining hydrocarbon mixtures are between about 250- 350 F., and more preferably between about 275-325 F. Extraction will occur, however, over a wide range of temperatures, e.g. 75-400 F., with varying degrees of success depending upon the particular feedstocks used. The extractor temperature should not exceed the boiling point of the aromatics-containing hydrocarbon mixture or the particular aqueous solution of 2-(2-aminoethoxy) ethanol employed, at the particular pressures employed.

Stripper bottoms temperatures should be sufiicient to eliminate hydrocarbons from the aqueous solvent system and typically are between about 250-350 F., and more preferably between about 260330 F.

Although pressure is not critical to this invention, it is preferable to contact the extraction process at a pressure sufiicient to insure that the raflinate does not vaporize, e.g. typical operations employ a pressure of about 50 p.s.i.g. above the vaporization pressure of the raffinate. A typical extractor pressure is between about 130-150 p.s.i.g.

The typical volume ratio of aqueous solvent solution to aromatics-containing hydrocarbon mixture fed to the extractor can vary between about 1/1 and 10/ 1, but is typically between about 2.5/1 and 5/1, or higher. Good results in most aromatics-containing hydrocarbon mixtures are obtained when this ratio is between about 3.5/1 and 4.5/1. The reflux stream from the stripper which is fed to the bottom of the extractor is typically between about 30-100 percent of the aromatics-containing hydrocarbon mixture fed to the extractor, by volume. Most preferably, it is between about 5 0-75 percent.

Typically, the rafiinate contains about 2-3% dissolved aqueous solvent, but by employing well known techniques,

including knock-out and water wash, this content can be reduced to less than about 1 ppm, by volume.

DESCRIPTION OF SPECIFIC EMBODIMENTS Specific examples of the practice of this invention are given below.

Example 1 The following data set forth in Table I below was obtained at ambient temperature (75 F.) by merely introducing five volumes of solvent solution and one volume of an aromatics-containing hydrocarbon mixture into a standard glassware separatory funnel having a capacity of about ml. Typically, the actual volume of aromaticscontaining hydrocarbon mixture was about 20 ml. The funnel containing the solvent (which was 2-(2-aminoethoxy) ethanol containing varying amounts of water) and hydrocarbon was mildly agitated by shaking between 20 minutes and one hour and thereafter allowing the hydrocarbon phase (raffinate) and solvent rich phase (extract) to separate by standing. The two phases were thereafter separated and analyzed using standard fluorescent indicator analysis (FIA) and ultra-violet procedures. In each run, the 2-(2-amin0ethoxy) ethanol content (mole/ liter) in the raffinate was less than 0.62 and did not increase as a function of water addition.

The hydrocarbon mixture used contained 43.8% aromatics by volume (by FIA); had a specific gravity of 0.7732 and the following boiling point characteristics:

The results obtained using the above described procedures are as follows:

TABLE I Solvent, vol. percent Extract, water in vol. percent 2-(2-annnohydrocarbons ethoxy) ethextracted from anol solvent hydrocarbon Run number solution mixture In Run Nos. 1-4, the molar ratio of aromatics in the extract to aromatics in the raffinate varied between 0.17- 0.20 while this ratio in Run No. 5 was 0.09. Since the data in Table I shows that the hydrocarbon percent extracted in Runs Nos. 1-4 stayed essentially the same and since the molar ratio of aromatics in the extract to aromatics in the raflinate stayed essentially the same, (i.e. 0.17-0.20) Example 1 shows that the capacity for aromatics of an aqueous solution of 2-(2-aminoethoxy) ethanol is not substantially affected up to about 5%, by volume water for this particular feedstock. Run No. 5 shows that the capacity of the solvent solution for aromatics in this particular hydrocarbon mixture was adversely affected by a water content of 10%, by volume.

equal parts, by weight, of aromatics and non-aromatics. As can be seen, the aromatics content of the feed is essentially composed of benzene, toluene and xylenes. The feed characteristics are reported in Table 11 below.

TABLE II Feed characteristics Volume percent distilled: F. IB'P 145 F=BP 340 Composition: Weight percent Non-aromatics 49.59 Heavy Aromatics 0 2.26 Benzene 18.06 Toluene 19.18 C Aromatics 10.77

The runs were conducted using a modified commercially available carbon steel York-Scheibel extraction column having an ID. of 3 inches and a height of 48 inches with thirty-six extraction stages spaced one inch apart, the first stage being located six inches from the bottom of the column and the thirty-sixth stage being located six inches from the bottom of the column and the thirty-sixth stage being located six inches from the top of said column, each said stage being comprised of a one inch diameter impeller rotating at 613 r.p.m. on a com mon shaft. Twenty-five cm. min. of feed was introduced into the column at stage number six and countercurrently contacted with one hundred cm. /min. of solvent which was introduced into the column just above the thirty-sixth tray. Raflinate was drawn off overhead from the column and twenty-five cm. min. of a reflux from stripping nonaromatics from the aromatics-rich extract leaving the extractor was introduced into the column just below the first stage. The extraction temperature Was 300 F. and all the conditions described above were held constant and the same feed composition was fed at the same rate while varying the water content of the solvent from 0% to 10%, by volume. The weight percent of aromatics and non-aromatics in the rafiinate and extract for varying amounts of water content in the solvent, using gas chromatography to analyze at the end of a twenty hour run for each specific variation of water, is set forth below using a solvent free basis, as is the percent BTX removed from the feed.

RUN 1 [Solventz Z-(Z-aminoethoxy) ethanol with no water] Rafiinate Extract Non-aromatics 89. 94 42. 41 Aromatics 10. 01 57. 58

This is a BTX removal from the feed of 91.52%, by weight, and 57.2% BTX in the extract, by weight on a solvent free basis.

This is a BTX removal from the feed of 92.5%, by weight and 63.3% BTX in the extract, by weight on a solvent free basis.

RUN III [Solventz 2-(2-aminoethoxy) ethanol with 4.2% water, by volume] Raffinate Extract fiJQ'fJtlEEY FFIIIII 33 $5: 33

This is a BTX removal from the feed of 91.8%, by weight and 69.4% BTX in the extract, by weight on a solvent free basis.

RUN IV [Solvent 2-(2-aminoethoxy) ethanol with 6% water, by volume] Raifinate Extract 585588518 3332: 5%: 2% $2: 2?

This is a BTX removal from the feed of 85.83%, by weight and 74.4% BTX in the extract, by weight on a solvent free basis.

This is a BTX removal from the feed of 75.83%, by weight and 82.8% BTX in the extract, by weight on a solvent free basis.

RUN VI [Solvent 2-(2-aminoethoxy) ethanol with 9.8% water, by volume] Raflinate Extract $Yi133333333 53:32 33:53

This is a BTX removal from the feed of 70.58%, by weight and 85.2%v BTX in the extract, by weight on a solvent free basis.

As can be seen, the percent non-aromatics in the extract, which in Run 1 was 42.41% (using 2-(2-aminoethoxy) ethanol with no water), decreases linearly with water addition to a low of 14.19% non-aromatics in Run No. VI (using 2-(2-aminoethoxy) ethanol solution containing 9.8% water, by volume). This data clearly establishes that the selectivity of an aqueous solution of 2-(2- aminoethoxy) ethanol, i.e. the preference for aromatics over non-aromatics, increases throughout the range of water addition up through 10% water.

The above data also establish that the capacity of the solvent solution is substantially unafiected over a certain range of water addition. In Run 1, the percent BTX removed is 91.52% using no water. In Runs II and III, using 1.9% water and 4.2% water, respectively, the percent BTX removed is substantially unchanged, being 92.5% and 91.8%, respectively. Not until Runs IV and V, using a water content of 6% and 8.55%, respectively, does the capacity fall off to any degree, being 85.83% and 75.83%, respectively. Thus, under the conditions shown, capacity of the aqueous 2- (Z-aminoethoxy) ethanol solvent solution is substantially unaffected by water addition up to about 5% water, by volume.

Example 3 In this example, seven runs were conducted using a feed comprised of about equal parts, by weight, of aromatics and non-aromatics. The feed characteristics are reported in Table III below.

7 TABLE III Feed characteristics Volume percent distilled: F. IBP 146 162 10 166 233 247 FBP 322 Composition: Weight percent Non-aromatics 49.23 Heavy aromatics C 0.57 Benzene 23.85 Toluene 23.20 C aromatics 3.12

The runs were conducted using a modified commercially available carbon steel York-Scheibel extraction column having an I.D. of 3 inches and a height of 90 inches with seventy-two extraction stages spaced one inch apart, the first stage being located six inches from the bottom of the column and the seventy-second stage being located ten inches from the top of said column, each said stage being comprised of a one inch diameter impeller rotating at 6 13 r.p.m. on a common shaft. Twenty-five cmfi/min. of feed was introduced into the column at stage number six and countercurrently contacted with one hundred cm. /min. of solvent which was introduced into the column just above the seventy-second tray. Rafiinate was drawn off overhead from the column and twenty-five cm. /min. of a reflux from stripping non-aromatics from the aromatics-rich extract leaving the extractor was introduced into the column just below the first stage. The extraction temperature was 300 F. and all the conditions described above were held constant and the same feed composition was fed at the same rate while varying the water content of the solvent from 0.7 to 12%, by volume. The weight percent of aromatics and non-aromatics in the raffinate and extract for varying amounts of water content in the solvent, using gas chromatography to analyze at the end of a twenty hour run for each specific variation of water, is set forth below using a solvent free basis, as is the percent BTX removed from the feed.

RUN I [Solventz 2-(2-arninoethoxy) ethanol with 0.7% water, by volume] Raffinate Extract Non-aromatics 09. 64 52. 56 Aromatics O. 33 47. 42

This is a BTX removal from the feed of 99.71%, by weight, and 46.85% BTX in the extract, by weight on a solvent free basis.

This is a BTX removal from the feed of 99.79% by weight and 60.11% BTX in the extract, by weight on a solvent free basis.

BUN III [Solvcntz 2-(2-aminoethoxy) ethanol with 5.5% water, by volume] Ratllnate Extract N oil-aromatics 99. G0 27. 22 Aromatics 0. 37 72. 76

8 This is a BTX removal from the feed of 99.77%, by weight and 72.45% BTX in the extract, by weight on a solvent free basis.

RUN 1V [Solventz 2-(2-aminoethoxy) ethanol with 8.17% water, by volume] Ralfinate Extract Non-aromatics 99. 0t 23. 78 Aromatics 0. 03 76. 21

This is a BTX removal from the feed of 99.30%, by weight and 75.86% BTX in the extract, by weight on a solvent free basis.

RUN V [Solvcntz 2-(2-aminoethoxy) ethanol with 10.17% water, by volume] Raflinate Extract Non-aromatics 98. 92 10. 36 Aromatics 1. 03 80. 62

This is a BTX removal from the feed of 99.33%, by weight and 80.23% BTX in the extract, by weight on a solvent free basis.

This is a BTX removal from the feed of 97.97%, by weight and 85.21% BTX in the extract, by weight on a solvent free basis.

RUN VII [Solvents 2-(2-aminoethoxy) ethanol with 12.07% water, by volume] RaIImate Extract Non-aromatics 95. 61 1. 85 Aromatics 4. 30 88. 13

This is a BTX removal from the feed of 96.11%, by weight and 87.94% BTX in the extract, by weight on a solvent free basis.

As can be seen, the percent non-aromatics in the extract, which in Run I was 52.56% (using 2-(2-aminoethoxy) ethanol with 0.7% water) decreases linearly with water addition to a low of 11.85% non-aromatics in Run No. VH (using 2-(2-aminoethoxy) ethanol solution containing 12.07% water, by volume). This data shows again that the selectivity of an aqueous solution of 2-(2-aminoethoxy) ethanol, i.e. the preference for aromatics over non-aromatics, increases throughout the range of water addition.

The above data also establish that the capacity of the solvent solution is substantially unaffected over a certain range of water addition. In Run I, the percent BTX removal is 99.71%, using 0.7% Water. In Runs II-V, the percent BTX removal never drops below 99.30% (from the 99.71% removal in Run I). This data shows that, for the particular feedstock used, the capacity of an aqueous solution of 2-(2-aminoethoxy) ethanol is not substantially affected throughout the range of 0.710% water, by volume. As can also be seen, the percent BTX removal in Run VII drops to 96.11% using 12.07% water.

A comparison of the feedstocks employed in Examples 2 and 3 disclose that the hydrocarbon content of the feed used in Example 2 contained about 13%, by weight, of aromatic heavier than toluene while the feed used in Example 3 contained about 3.5% of aromatics heavier than toluene. Thus, depending upon the particular aromatic compounds in the aromatic-containing hydrocarbon mixture to which the extraction is directed, the amount of water that the aqueous solution of 2-(2-aminoethoxy) ethanol can tolerate before capacity is adversely affected can vary considerably. As before stated, however, the capacity of an aqueous solution of 2-(2-aminoethoxy) ethanol for aromatics in the vast majority of aromatic-containing hydrocarbon mixtures will be substantially unaffected by a water content in the range of from about 0.7 to some value less than about 10 percent, by volume, depending upon the particular aromatics involved.

We claim:

1. A process for extracting aromatics from a naphtha feed stock which comprises contacting said naphtha feed stock with an aqueous solution of 2-(2-arninoethoxy) ethanol containing from about to percent water, by volume, for a time sufiicient to extract substantial quantities of aromatics from said naphtha feed stock having the percentage of the sum of benzene and toluene in said feed stock high enough so there is no decrease in capacity in adding up to 10 percent water in said 2-(2-amin0- ethoxy) ethanol.

2. A process as described in claim 1 wherein the aqueous solution contains between about 5-9 percent water, by volume.

3. A process as described in claim 1 wherein the aqueous solution contains between about 5-8 percent water, by volume.

4. A process as described in claim 1 wherein the extract and the raflinate are thereafter separated.

5. A process as described in claim 2 wherein the aromatics-containing hydrocarbon mixture and aqueous solution are contacted countercurrently in an extractor in a manner such that the volume ratio of aqueous solution to said mixture is between about 1/1 and 10/1.

6. A process as described in claim 5 wherein the extraction occurs at a temperature between about 250-350 F.

7. A process as described in claim 6 wherein substantially all of the hydrocarbons are removed from the ex- 10 tract and the remaining aqueous solution of Z-(Z-aminoethoxy) ethanol is adjusted to contain between about 5-10 percent water, by volume, and recycled to the extractor.

8. A process as described in claim 7 wherein the nonaromatic hydrocarbons removed from the extract are recycled to the extractor, the amount of said non-aromatic hydrocarbons being about 30-100 percent, by volume, of said mixture.

9. A process as described in claim 8 wherein the aromatics in said mixture contains benzene, toluene, xylenes, or mixtures thereof.

10. A process as described in claim 9 wherein the extractor temperature is between about 275-325 F.; the volume ratio of said solvent to said mixture is between about 2.5/1 and 5/1; the extract is flashed at least once prior to .being fed to a stripper which is being operated at about 260-330 F.; and the raflinate is water washed to remove a portion of the aqueous solvent contained therein.

References Cited UNITED STATES PATENTS 3,415,739 12/1968 Eisenlohr et al. 260-674 SE 2,838,582 6/ 1958 Kassel et al. 208-324 3,583,906 6/1971 Basila et al. 208-33l 2,280,264 4/1942 Reeves 208-324 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

